Problems after Speedball upgrade. Right channel dead and smoke.

[orri]

Hi,

I completed my Crack without any significant problems  and enjoyed it for about a week when I decided it was time for some speedball.

The installation went well and I listened to it for about an hour when all of a sudden the right channel died and (I think) the sound from the left became quieter. I then started feeling a smell like something had burnt so I unplugged the power cord. After a while I turned the Crack over but couldn't see anything noticeable and at this point I was too tired to troubleshoot for the problem.

So the next day I plugged the Crack back in and took out the DMM to do the voltage checks. After about a minute with the Crack turned on I started feeling that smell again and then I saw smoke coming from (I think) the 220uF cap at terminals 14 & 15. So I quickly turned off and unplugged the Crack again.

Since this is my first DIY project I have no idea what could be wrong and was hoping to get some help from here.
Could it speedball related or just a bad cap?

All help would be very welcome.

Cheers,
Orri

 

[Doc B]

First check that the electrolytics capacitors were all installed in the proper orientation. Then carefully go over the wiring changes you made during the addition of the speedball, making sure every wire coming off of every board is cnnected to the correct terminal. Then check to see if every transistor is on the correct PC board and that the MJE 350s are facing the right way.

 

[orri]

Thanks Doc.

I rechecked all the solder joints on the PC boards and it seems like I had a bad joint from 3U to the G pad on the right side of the PC board (the second to last joint in the manual).

I then took a deep breath and plugged in and turned on the Crack and waited a while to see if there would be any smoke. Fortunately there wasn't so I did the voltage check and everything was OK except for terminal 19 and 20. 19 is supposed to be 0 but was instead 79.5. Terminal 20 is supposed to read 206 but was -16v. Instead, terminal 21 was 206.
I'm not sure but I think these must be the same numbers I got originally.

I tried to plug in my headphones and I'm very glad to report that I get sweet music from both channels.
I guess this means my Crack is OK but I can't help but think about the smoke and smell I got earlier as well as the voltage check numbers.

Is there anything I should recheck or be worried about?

Orri

 

[Laudanum]

21 is supposed to measure 206 volts.  But no near terminal is supposed to read around 80 volts.  Im not one of the gurus here but you may want to re-check the orientation, spacing and correct installation points of the diodes on that terminal strip.  I wouldnt plug headphones in again until you carefully verify while referencing the manual and re-do all voltage checks.

 

[orri]

Well, according to the Crack manual, terminal 20 is supposed to measure 0 and 21=206. But accroding to the Speedball manual, 20 is supposed to measure 206 and there is no mentioning of 21.

I assume I should use the numbers from the Speedball manual unless there is a typing error in either one?

 

[Doc B]

It is always worth it to read the sticky posts we put in each product forum -

http://www.bottlehead.com/smf/index.php/topic,1398.0.html

 

[orri]

So I should be OK then, Doc? At least the Crack is working and sounds wonderful

What about the smell and the smoke? What could that have been?

 

[Doc B]

Yeah you are probably fine. From your descripton the smell was probably from excess current going thru the 270K resistor across the filter cap when the PC board ground was not connected. Examine the resistor to see if it looks cooked. If not it is probably fine. You would need to disconnect one end of it from the circuit to measure it if you are so inclined.

 

[orri]

Everything looks fine and sounds fine so I guess my problems are solved.

Thank you so much for your help.

Back to the addiction...